1. Field of Invention
The present invention relates to a wet metal-etching method adapted to be used for 6 inches or above micro-machining process, and more particularly to a wet metal-etching method adapted to be used for micro-machined device with high requirement of etching uniformity.
2. Description of Related Arts
With the development of the science and technology, electro-mechanic devices are becoming more and more compact, integrated and intelligent. Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and electronic circuits on a common silicon substrate through micro-fabrication technology. While the electronics are fabricated using integrated circuit (IC) process sequences (e.g., CMOS, Bipolar, or BiCMOS processes), the micromechanical components are fabricated using compatible “micromachining” processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices.
In order to form components on a substrate, it is necessary to selectively etch the thin films previously deposited on the substrate. Wet etching works very well for etching thin films on substrates, and can also be used to etch the substrate itself. The problem with wet etching is that its isotropic character will cause overetch of the thin film under the mask layer. The overetch, even less than 1 μm, is unacceptable for the ULSI, because it will results in a loss of space. Therefore, dry etching with anisotropic character is commonly adopted by the semiconductor manufacturer. In most cases, however, space is not so critical for MEMS devices because of its low integrity, and, in addition, dry etching is much more expensive compared to wet etching. Furthermore, many materials used in MEMS, especially metal material, such as NiCr, Au, Cu and so on, are not compatible with the semiconductor process, and can not be etched by dry etching process. In comparison, almost all metal materials can be etched via wet etching process and all kinds of metal etchants are already available in the market.
However, the overetch, especially non-uniform overetch is still a serious problem in the wet metal-etching process, especially for large diameter silicon wafer, such as 6 inches (and above) wafer. Therefore, an improved wet metal-etching process that ensures a uniform etch over whole wafer is highly desirable.